Estimating Individual and Combined Fingertip Forces From Forearm EMG During Constant-Pose, Force-Varying Tasks

Numerous applications in areas such as ergonomics assessment, clinical biomechanics and motor control research would benefit from accurately modeling the relationship between forearm EMG and fingertip force, using conventional electrodes. Herein, we describe a methodological study of relating 12 conventional surface EMGs, applied circumferentially about the forearm, to fingertip force during constant-pose, force-varying (dynamic) contractions. We studied independent contraction of one, two, three or four fingers (thumb excluded), as well as contraction of four fingers in unison. Using regression, we found that a pseudo-inverse tolerance (ratio of largest to smallest singular value) of 0.01 was optimal. Lower values produced erratic models and higher values produced models with higher errors. EMG-force errors using one finger ranged from 2.5–3.8% maximum voluntary contraction (MVC), using the optimal pseudo-inverse tolerance. With additional fingers (two, three or four), the average error ranged from 5–8 %MVC. When four fingers contracted in unison, the average error was 4.3 %MVC.